The present invention relates to a locking device for mutually locking two elements, in particular a covering element to an element forming a support frame for this covering element, and applies for example to devices for closing shafts for inspecting an underground network, such as roadway or footway manholes, and to devices for closing technical inspection chambers of an underground cable network, such as trapdoors.
At present, there are numerous mechanical devices for making such covers or trapdoors tamper-proof, both of the lock type and of the latch type.
Locks include a mechanism which may be complex, causing the displacement of a bolt under a keeper by means of a specific key. They generally afford a relatively high level of security, but their complex mechanism, often situated in a environment which is corrosive and favourable to fouling, requires costly protection (xe2x80x9cnoblexe2x80x9d materials and leaktight housing).
Latches are simple and economical devices which are not very sensitive to the environment and are generally actuable by a key rotationally driving a pivot with a special head integral with a bolt movable under a keeper. They generally afford a lower level of security, the head of the pivot being visible and capable of manipulation by conventional tools.
The object of the invention is to overcome these disadvantages by creating a device of the latch type which is not very sensitive to fouling and corrosion and can easily be made invisible to the outside and inaccessible to conventional tools, so as to afford a level of tamper-proofing and security comparable to that of a lock.
To this end, the invention relates to a locking device for mutually locking a first and second element, in particular a covering element to an element forming a support frame for the covering element, of the type including a movable bolt and a key for actuating the bolt, characterised in that it further includes two bolt-guiding members carried by one of the said first and second elements, and the bolt includes a key-inserting aperture, two guiding ramps adapted to cooperate with the two guiding members respectively, and a third guiding ramp adapted to cooperate with the contour of the key when the latter is inserted into the said aperture, in order to selectively actuate the bolt from a locking position to an unlocking position or from an unlocking position to a locking position, by rotation of the key.
The fact that the actual latch consists of few members also makes it very economical.
The locking device according to the invention may further have one or more of the following characteristics:
one of the bolt-guiding members is carried by the first element and is formed by a member for securing the bolt to the first element, and the guiding ramp adapted to cooperate with this member is a wall of an oblong hole which is made in the bolt and into which the securing and guiding member is inserted;
the securing and guiding member is a screw, the body of which is passed through the oblong hole and carries a locknut situated under the bolt;
the other bolt-guiding member is carried by the first element and formed by a wedge-shaped finger, and the guiding ramp adapted to cooperate with this member is a region of a lateral edge of the bolt including an indentation forming a receptacle for the finger;
the wedge-shaped finger is in one piece with the cover and extends in a manner projecting from a bottom face thereof;
the third guiding ramp adapted to cooperate with the contour of the key consists of the lateral wall of the aperture, this lateral wall being adapted to cooperate with a key bit when the latter is inserted into the aperture;
the aperture has an indentation, one edge of which forms an abutment for the bit when the bolt is in the unlocking position;
the bit has a notch adapted to come into engagement with a boss in the shape of a circular crown surrounding a hole for inserting the key, made in the cover and situated facing the aperture, this boss projecting into the aperture and also cooperating with the third guiding ramp;
the hole has a frustoconical shape flared towards the outer face of the cover and adapted to cooperate with a complementary frustoconical surface of the key, so as to ensure the rotational guidance of the key;
the frustoconical hole has a major diameter significantly smaller than the aperture; and
the key includes, at the base of a shank, a collar intended to bear on the cover, and the region for connection of the bit to the collar has a frustoconical surface adapted to cooperate with a frustoconical surface of a hole of the cover.